The present invention concerns a circuit for stabilizing high voltage according to the change of the horizontal oscillating frequency, wherein a constant high voltage is obtained regardless of the change of at least two horizontal oscillating frequencies applied to a cathode ray tube (CRT).
Conventionally, the high voltage generating circuit of a CRT keeps a constant high voltage regardless of the change of the horizontal frequency or the beam current, and drives the horizontal output stage at a single horizontal frequency. However, as apparatuses such as a computer become to have a variety of functions, it is necessary for them to operate at two or more horizontal frequencies, where regardless of the horizontal frequency changes must be obtained a constant high voltage.
One of such conventional apparatuses is disclosed in Korean Utility Model Publication No. 89-5450 issued on Aug. 18, 1989, which is illustrated in FIG. 2 attached to the present application. According to this high voltage stabilizing circuit, a direct current source 1 is connected to the collector of voltage control transistor TR1, between whose collector and base is connected resistor R1. The emitter of the transistor TR1 is connected to the primary coil of flyback transformer FBT, whose secondary coil has a high voltage rectifying diode D1, whose cathode in turn is connected through a resistor R3 to a variable resistor R4. The intermediate terminal of the resistor R4 is connected to the non-inverting terminal(+) of an operational amplifier OP1, which has an inverting terminal(-) connected to the output thereof, which in turn connected to the base of a second transistor TR2, which has the collector connected to the base of the first transistor TR1. A third horizontal drive transistor TR3 connected to a horizontal oscillating circuit 3 is connected through a transformer T1 with a fourth horizontal output transistor TR4 connected to the other end of the primary coil of the flyback transformer FBT. A fifth transistor connected to the horizontal oscillating circuit 3 is connected through another transformer T2 to a sixth transistor TR6 of a saw tooth generating circuit connected to a deflection yoke coil DY. The high voltage change produced in the high voltage rectifying diode D2 of the flyback transformer FBT is detected through a third resistor R3, which change causes the output voltage of the operational amplifier OP1 to change, thereby changing the base voltage of the first voltage control transistor TR1 so as to keep constant the flyback pulse voltage Vcp generated from the collector of the fourth horizontal output transistor TR4.
In such a conventional high voltage stabilizing circuit, the change of the high voltage caused by the horizontal frequency change is detected through the anode terminal, so that the flyback transformer FBT is specially prepared because the voltage applied to the anode is at least 25KV.
Consequently, the very high voltage detected needs the constituent elements capable of tolerating it, and moreover makes the circuit design difficult.